iCloud lying about my drive storage

My iCloud account started complaining my storage was full (I have the 200GB plan), when it shouldn't. I deleted an iPhone backup of ~80GB so I could see more info, and that's what I see now (same info on the Mac, the iPhone and iCloud.com):

When browsing iCloud Drive files (again all platforms), there is ~nothing. I've opened all folders one by one and their total size is WAY less than 1GB, which iCloud reports over 100GB usage.

It's not photos, not backups, not family usage (as they all have a dedicated category) nor app usages as far as I can tell.

What else could be using iCloud Storage space? Is it possibly an iCloud bug?